I had a rough night playing in a dark stage yesterday. The Sound guy thought it would be cool to fart around with the lights and leave them off for the most part. Well needles to say I couldn't see my hand position and were I was on the fretboard and I was hitting quite a few bad notes. Other then practicing in the dark are there any ways to avoid this situation? Does any use Led position markers? Is it worth it? How much does it cost?